1. Field of the Invention
The present invention relates to thermosetting acrylic copolymer compositions for use in coating applications. More particularly, this invention relates to thermosetting acrylic compositions in which the acrylic copolymer contains active hydrogens and is in combination with a curing agent such as an amine-aldehyde condensate capable of reacting with the active hydrogens at elevated temperature to form a thermoset coating.
2. Brief Description of the Prior Art
Coating compositions based on acrylic polymers are well known in the art. The coatings are hard, curable and have excellent humidity resistance making them particularly desirable as exterior or topcoats for the automotive (including truck) market. Both thermoplastic and thermosetting acrylic polymers are employed for this use. However, for the automotive market, the acrylic polymers are organic solvent-based and present environmental problems with regard to solvent emissions. These problems can be overcome by using water-based acrylic polymers; but, until the present invention, water-based acrylics have not been considered acceptable for automotive topcoat applications. It had been thought that water-based acrylic polymers had poor rheological properties and had insufficient gloss and humidity resistance for automotive topcoat use. Surprisingly, it has been found that certain water-based acrylic polymers of a specific molecular weight range and prepared with a specific class of higher alkyl esters of alpha, beta-ethylenically unsaturated carboxylic acids can be used in aqueous-based thermosetting compositions for automotive topcoats. The resultant coating compositions have good rheological properties and sufficient gloss and humidity resistance for automotive usage. The thermosetting coating compositions of the present invention can be applied as aqueous-based compositions at high solids contents with good metallic pigment pattern control, gloss and distinctness of image (DOI).